The invention described herein relates generally to image sensor devices and the methods of their manufacture. In particular, the invention relates to methods and structures for creating image sensors devices having curved surface contours.
A commonly used conventional image sensor device 100 is schematically depicted in the simplified illustration of FIG. 1. Typically, a substrate 101 has an array of photodiodes 102 (also referred to as xe2x80x9cphoto arraysxe2x80x9d or xe2x80x9cphotoimagersxe2x80x9d) formed on the surface of the substrate 101. The methods of forming such photo arrays are well known to those having ordinary skill in the art. Typically, the substrate 101 is mounted to a flat support structure 103 and electrically connected to a plurality of electrical contacts. In the depicted example, the substrate 101 is electrically connected to bond pads 105 of the support structure 103 using wires 104 (e.g., using wire-bonding techniques). The structure is then enclosed in a package 106 with a light transmissive surface 107 that allows light to impinge on the array of photodiodes 102 formed on the surface of the substrate 101. Typically, the foregoing structure 108 is coupled with a lens 110 to improve optical performance.
One of the problems of such photoimagers is that the lenses required to obtain high quality images are relatively expensive. In order to produce a flat image with relatively little distortion or little chromatic aberration requires the implementation of multiple lenses which are arranged to generate a flat optical plane. This can require many expensive optical elements.
Inexpensive lenses are available but they exhibit some undesirable optical properties. One problem is illustrated with respect to FIG. 2 which schematically depicts one type of readily available low cost lens 201. The depicted representation is merely illustrative and is neither to scale nor intended to be strictly limited to any particular lens embodiment. Incident light 202 is received and focused by the lens 201. Such lenses are very effective for focussing light on a single point. However, they are rather less effective at focussing the light at every point in a flat focal plane (depicted here by the flat line 203). Such lenses 201 tend to generate focal surfaces that are not planar (flat).
The focal surface of a lens is defined by a plurality of focal points for the lens wherein light passing through the lens is in focus at each point on the focal surface. In the example depicted in the cross-section view of FIG. 2, a plurality of focal points 205 defines a curved focal surface 204 for the lens 201. The degree and type of curvature is dependent on the lens properties. In some embodiments the focal surface can be parabolic or in others the focal surface can be spherical or cylindrical having a common radius of curvature. Other more complex focal surfaces can also be generated.
Such single element lenses, although inexpensive and relatively easy to manufacture, do not generate flat focal planes. As result, when used with flat image sensors image quality is degraded. This image deterioration is especially severe around the edges of such image sensors. For these and other reasons, such lenses are not generally suitable for use with flat image sensors. Until now, the only solution to these problems has been the implementation of complicated multi-lens structures to generate a flat focal plane that can be used to project light onto the flat surfaces of the photoimagers. Although optically suitable, such implementations have the disadvantage of being much more expensive than single lens element implementations.
What is needed is an image sensor module that can utilize these low cost single element lenses without suffering from excessive degradation of image quality. Also needed are methodologies for fabricating such structures. The principles of the present invention are directed toward an improved image sensor module and methodologies for it fabrication.
In accordance with the principles of the present invention, the invention includes an image sensor module and methods for its fabrication.
An image sensor module embodiment having a photoimager with a curved surface and methods for its fabrication are disclosed. The image sensor module includes a flexible support with sufficient flexibility so that it can be shaped into a curved configuration. The substrate includes optical circuitry on its surface and is formed sufficiently thin so that it can be shaped into a curved configuration. The substrate is coupled with the flexible support to form a combination can be shaped into a curved configuration that matches a curved focal surface of a lens. This embodiment can be mounted inside an optically transmissive housing and optically coupled with a suitable lens.
In another embodiment, an optical sensor module comprises a rigid support having a curved surface contour that substantially corresponds to a curved focal surface of a lens. A substrate having optical circuitry formed on its surface is provided. The substrate is formed sufficiently thin so that it can be formed into a curved configuration. A lens having a curved focal surface is also provided. The substrate is coupled with the curved surface contour of the rigid support and mounted with the lens such that the optical circuitry of the substrate obtains a curve that substantially matches that of the focal surface of the lens.
In another embodiment the invention comprises a method for forming a curved image sensor. The method includes providing a substrate with optical circuitry formed on a front side, bulk removing material from the back side of the substrate, and precision removal of material from the back side of the substrate until the substrate has a desired thickness enabling the substrate to be shaped into a curved configuration. The substrate is then singulated and coupled with a support. Where the support is rigid, the coupled substrate and support can be mounted with a hosing an optically coupled to a lens. Where the support is flexible, the coupled substrate and flexible support can be curved to match a lens and mounted in a housing.
These and other aspects of the invention will be disclosed in greater detail in the following detailed description.